1. Field of the Invention
The present invention generally concerns devices, methods, imaging systems and media for radiatively recording (writing) and radiatively reading digital data within the three-dimensional volume of optical media, principally optical disks.
The present invention particularly concerns a (i) two-photon (two-beam) writing method, and single-photon (single-beam) readout method, using a (ii) doubly-telecentric afocal imaging system for the (iii) massively parallel recording (writing) and (iv) reading of digital data within the three-dimensional volume of an optical medium, preferably a rotating optical disk containing a photoactive chemical.
The present invention still more particularly concerns a digital video/versatile disk (xe2x80x9cDVDxe2x80x9d), compact disk (xe2x80x9cCDxe2x80x9d) any kind of optical disk (generically xe2x80x9cCDsxe2x80x9d) in which digital data storage is three-dimensional (3-D), thus a xe2x80x9c3-D CDxe2x80x9d.
Key words to the present invention include: optical memory; three-dimensional memory; volume memory; two-photon memory; multilayer imaging; depth transfer objective (xe2x80x9cDTOxe2x80x9d); DTO with a non-immersed detector; DTO with an immersed detector; DTO with aberration correction; Non-1:1 DTO imaging systems; doubly telecentric imaging; afocal imaging; 4-f imaging configurations; three-dimensional optical or compact disks (xe2x80x9c3-D CDsxe2x80x9d); and three-dimensional Digital Video Disks or Digital Versatile Disks (xe2x80x9c3-D DVDsxe2x80x9d).
2. Description of the Prior Art
2.1 General Background
Information processing applications once in the realm of supercomputing (e.g., 3-D visualization, virtual reality, data mining) are now moving to the desktop and even to mobile computing platforms. This rapid evolution of the information age has led to an explosive growth in the demand for high-capacity/high-performance secondary storage. Optical storage has been a candidate to meet this demand for some time. The optical disk, most particularly the compact disk (CD) and the newer Digital Video Disk (DVD) (sometimes called Digital Versatile Disk), are successful forms of inexpensive mass digital data storage. Although optical storage has greatly evolved, so also has the magnetic, Winchester, disk evolved greatly. Moreover, magnetic recording is still rapidly evolving, including by new exploitation of the giant magnetorestrictive effect.
The strengths of optical recording and recording mediaxe2x80x94large storage capacities and low costxe2x80x94will likely ensure the perpetuation of this method and media into the foreseeable future. However, an even larger role for optical recording, and media, could be foreseen if, while preserving and even enhancing its present strengths, optical recording was to draw closer to or, preferably, even exceed the performance of magnetic recording in any of (i) gross capacity, (ii) cost per bit stored, (iii) seek, or latency, time, (iv) sustained data transfer rate for both reading and writing, and (v) reusability, and longevity. At the present time (circa 1998) many things differ between optical and magnetic storage. The weights, sizes and power consumption of optical and magnetic disk drives are slightly different. One or another media can, in one form or another, store more (or less) than forms of the other media. Optical disks have generally had, until recently, similar or greater capacity per disk platter than magnetic disks. However, the tiny size of the heads of magnetic disks permits many disk plattersxe2x80x94typically 14 to 16 in present-day 49 Gbyte capacity drivesxe2x80x94to be stacked on one spindle with a head on each side of each disk platter, thus greatly increasing the overall capacity of a magnetic disk drive over an optical disk drive. On the other hand, optical disks have typically offered lower cost for high capacity, easy removability, and long archival lifetimes.
Data transfer rates are commensurate for magnetic and for optical disks. However, latency times to access data on a spinning magnetic disk are presently superior to those of an optical disk. Additionally, those generally more expensive forms of optical disk that can be written at all can generally be written only but much slower than can magnetic disks, and often for only but a limited number of times.
The present invention will soon be seen, by effectively xe2x80x9cstackingxe2x80x9d optical disk platters, to greatly change many of these previous relationships of cost, speed and latency. However, antecedent activities to the present invention are first discussed.
To meet the demand for high-performance optical digital data storage, there are two main trends apparent in present-day (circa 1998) research and development. Volumetric storage and data channel parallelism together are the key routes to achieving the capacities and transfer rates needed in future military and commercial applications. Both of these techniques require the development of novel parallel optical pick-up heads. See K. Kayanuma, T. Iwanaga, H. Inada, K. Okanoue, R. Katayama, K. Yoshihara, Y. Yamanaka, M. Tsunekane, O. Okada, xe2x80x9cHigh track density magneto-optical recording using crosstalk canceler,xe2x80x9d Proc. SPIE 1316, 35 (1990). See also T. Maeda, H. Sugiyama, A. Saitou, K. Wakabayashi, H. Miyamoto, and H. Awan, xe2x80x9cHigh-density recording by two-dimensional signal processing,xe2x80x9d Proc. SPIE 2514,70(1995). See also S. Gopalaswamy and B. V. K. V. Kumar, xe2x80x9cMultichannel decision feedback equalizer for high track density in optical recording,xe2x80x9d Opt Eng. 35,2386 (1996).
Recent developments in optical storage also include the evolution of CD-ROM technology to volumetric systems such as the 2-layer digital versatile disk (DVD) standard. The present invention will be seen to extend this concept to a technology enabling the recording and reading of disks having hundreds or thousands of layers, potentially leading to more than a 100 times increase in capacity. See F. B. McCormick, I. Cokgor, S. C. Esener, A. S. Dvornikov, and P. M. Rentrepis, xe2x80x9cTwo-photon absorption-based 3-D optical memories,xe2x80x9d in High Density Data Recording and Retrieval Technologies, Ted. A. Schwartz; Martin Francis, Editors, Proc. SPIE 2604,23-32(1996). See also I. Cokgor, P. B. McCormick, A. S. Dvornikov, M. M. Wang, N. Kim, K. Coblentz; S. C. Esener, P. M. Rentrepis, xe2x80x9cMultilayer disk recording using 2-photon absorption and the numerical simulation of the recording process,xe2x80x9d in Optical Data Storage ""97, 1997 OSA Technical Digest Series (Optical Society of America, Washington, DC, 1996).
2.2 Two-Photon Optical Processes
One embodiment of the optical storage in accordance with the present invention will be seen to rely on recording bits in a volume by process of two-photon absorption (i.e., xe2x80x9c3-D 2-Pxe2x80x9d). A spot is written in the volume of a molded organic polymer only at points of temporal and spatial intersection of two beams collectively having sufficient photon energiesxe2x80x94beam one carrying information (i.e., at 1064 nm) and the other intersecting so as to specify location (i.e., at 532 nm)xe2x80x94so as to change the optical property of a photochemical at the region of intersection, and nowhere else. The simultaneous absorption of photons from both beams results in a photochemical change in the active molecules doped into the polymer, which changes the absorption and fluorescence spectra of the material (though changes in refractive index, electrical characteristics, etc., may also be obtained with appropriately engineered dopant molecules).
The recorded bits are read by fluorescence when excited by single green photons absorbed within the written spot volume(s). By intersecting a sheet of light with a 2-D page of data bits, lines (vectors) or planes of data marks may be both written and, at other times, read, in parallel. Using this method, the assignee of the present inventionxe2x80x94Call/Recall Corporationxe2x80x94has demonstrated multiple image storage in read only memory (xe2x80x9cROMxe2x80x9d) configuration in a portable player unit. The results indicate no crosstalk between layers and excellent stability of the written bits at room temperature. As many as 100 layers have been stored in an 8 mm thick cube. See M. M. Wang, S. E. Esener, F. B. McCormick, I. Cokgor, A. S. Dvornikov, P. M. Rentzepis, xe2x80x9cExperimental characterization of a two-photon memory,xe2x80x9d Optics Letters 22(8), pp. 558-560 (1996)
A recent monolithic disk recording experiment has demonstrated 120 layer recording. Separate experiments have recorded layers as close as 30 xcexcm without crosstalk, with bit domains, or voxels, as small as 7 xcexcm diameter. Thus the fabrication of ultra-high capacity 3-D multi-layer disk appears feasible. However, to exploit this new storage media, a means to efficiently and cost effectively access the data stored throughout the volume of the disk is needed.
2.3 Optical Disks
Current multi-layer optical read techniques (e.g., for DVD optical storage disks) read a single track on a single layer. When access to data on another layer is necessary, the objective lens is moved to refocus onto that layer. This refocusing distance is typically less than 100 microns. However, it cannot generally be accomplished without a break in the data stream due to the need to reestablish the correct focus and accurate tracking on the new track, and to synchronize the data channel clock to the new data stream. Extension of this current technique to thick multi-layer having many recorded layers disks is problematic.
First, the many layers may be reasonably distributed within a thickness of 5-10 mm. To rapidly focus onto layers distributed over this large range would require a dynamic focus actuator of undesirable size, cost, and power dissipation.
Focusing over this large thickness range also introduces large amounts of aberration into the optical path. To maintain the high resolution required of these systems, an aberration control system with high speed and large dynamic range would be needed.
To efficiently use the high capacity offered by the multi-layer approach, it is also necessary to provide increased data transfer rates. A powerful means of increasing data transfer rates is to read multiple tracks simultaneously. However, reading more than one track at a time requires a lens with a larger field of view (xe2x80x9cFOVxe2x80x9d), where the FOV is typically defined as the lateral distance over which (i) the optical aberration is xe2x80x9cwell-correctedxe2x80x9d and (ii) the resolution is limited mainly by diffraction. Such wide field lenses are generally larger, heavier, and more expensive than the single-spot lenses used in optical storage systems today. Thus any new technique should seek to read the most data marks within the smallest two-dimensional FOV in order to limit this increased complexity and cost.
Parallel readout techniques for single layer media have been proposed and demonstrated which simultaneously read several tracks along a radius or a chord of the disk. However, scaling these approaches to large numbers of tracks is difficult, since the 1-D nature of the line of bits does not efficiently use the 2-D optical FOV. On the other hand, reading a 2-D array of marks from different regions requires that the should disk step from one 2-D page to the next, starting and stopping rather than rotating continuously. This introduces problems in accelerating and decelerating the disk, and in keeping the subsequent vibrations from affecting the data signal integrity.
2.4 Particular Prior Artxe2x80x94Optical Disks
The present invention, although applicable to volume optical memories of all geometric forms (such as, for example, cubical), will seen to preferably be embodied in an optical disk. Accordingly, the state of the art in accessing information within the volume of an optical disk is reviewed herein.
U.S. Pat. No. 4,450,553 for a MULTILAYER INFORMATION DISC to Holster, et al., and assigned to U.S. Phillips Corporation (New York, N.Y.) concerns a multilayer information disc, in particular a video disc, which is read by laser light. The disc comprises at least two radiation-reflecting optical structures each having a relief-like information track of regions situated alternately at a higher and a lower level which is read in reflection and on the basis of phase differences. Each of the optical structures is covered with a reflection layer at least one of which partially transmits the reading radiation so that upon reading the other optical structure or structures, the radiation passes through the structure provided with the partially transmitting reflection layer. The coefficients of reflection of the various reflective layers are preferably matched to each other in a manner such that upon reading the same amount of light returns from each optical structure. A suitable material for the partially reflective layer is a dielectric which has no light absorption.
U.S. Pat. No. 5,097,464 for an OPTICAL RECORDING MEDIUM AND OPTICAL RECORDING/REPRODUCING APPARATUS to Nishiuchi, et al., and assigned to Matsushita Electric Industrial Co., Ltd. (Osaka, Japan) concerns a data playback apparatus for reproduction of data from an optical recording medium which has a data layer disposed on a substrate thereof having a specific thickness is provided with an optical length corrector interposed between the recording medium and an objective lens for converging a light beam. The optical length corrector is selected so that the sum of the optical length od the optical length of the optical length corrector equals a predetermined length for the objective lens. Accordingly, the light passing the objective lens can converge on the data layer developing a light spot close to the limit of refraction, regardless of the thickness of the substrate of the recording medium.
U.S. Pat. No. 5,134,604 for a COMBINATION OPTICAL DATA MEDIUM WITH MULTIPLE DATA SURFACES AND CASSETTE THEREFOR to Nagashima, et al., and assigned to Matsushita Electric Industrial Co., Ltd. (Osaka, Japan) concerns an optical data medium from which information recorded to the surface is reproduced by focusing a laser thereon and reading the light reflected from the data surface. The medium includes a first transparent layer having a top data surface for carrying data, and a second transparent layer having a bottom data surface for carrying data. A semi-transparent layer is inserted between the first and second transparent layers. When the laser is focused on the top data surface, the data carried therein is reproduced, and when the laser is focused on the bottom data surface, the data carried therein is reproduced.
U.S. Pat. No. 5,163,039 for a THREE-DIMENSIONAL OPTICAL MEMORY SYSTEM to Lindmayera and assigned to Quantex Corporation (Rockville, Md.) concerns a three-dimensional optical memory system is disclosed which utilizes at least two layers of electron trapping media having different sensitivities to visible light coated on a substrate to store data in the form of light energy. Data is written onto the substrate, which may be in the form of a disk, which is contained in a light-tight contamination-free environment similar to a Winchester hard disk drive system, using at least two visible light laser beams having different wavelengths. Data is read from the disk using an infrared light laser beam. The at least two different data streams are separately detected. The system may be used as part of an optical disk drive system which is desini or 5xc2xc inch disk drive form factor for personal computers.
U.S. Pat. No. 5,414,451 for a THREE-DIMENSIONAL RECORDING AND REPRODUCING APPARATUS to Sugiyama, et al., and assigned to Hitachi, Ltd. (Tokyo, JP) concerns a three-dimensional recording and reproducing apparatus having a recording medium including a plurality of recording layers stacked on a substrate and an optical system for converging a light irradiated from the substrate side on each of the plurality of recording layers to three-dimensionally record and reproduce information. A light spot is focused on each layer of the multi-layer structured disc to record and reproduce highly reliable data in a high density. An equation relating the light wavelength, substrate refractivity, focal lens numerical aperture, and positional range in the optical axis on which exists a recording layer upon which light is converged, is satisfied.
U.S. Pat. No. 5,614,938 for a THREE-DIMENSIONAL RECORDING AND REPRODUCING APPARATUS to Sugiyama concerns a three-dimensional recording and reproducing apparatus having a recording medium including a plurality of recording layers stacked on a substrate and an optical system for converging a light irradiated from the substrate side on each of the plurality of recording layers to three-dimensionally record and reproduce information. The same equation as is satisfied for the above U.S. Pat. No. 5,414,451 to Sugiyama, et al. is again satisfied.
2.5 Particular Prior Artxe2x80x94Error Correction Codes, Particularly for Optical Storage
The present invention is not about error correction codes. Indeed, at certain domain dimensions and optical signal-to-noise ratios of the volume optical memory of the present invention, error correction is not required, and the successful implementation of the present invention does not in any substantial manner depend upon error correction codes. However, it is well known that both existing (i) semiconductor and (ii) magnetic computer memories constrain, and manage, the occurrence of error. Even if an optical memory were to be less, or much less, prone to error than competing semiconductor and magnetic forms of digital memory, it would be rash to talk about supplanting these existing forms with optical memory without explaining the management of such errors as may inevitably occur in optical memory.
The present invention opens up a practical application for the mathematical error correction of (optical) bits (optically) detected in a plane of bits, and typically very large planes of a million or more bits each successively read very fast, typically at perhaps one full bit plane, or page, every microsecond. The present section simply makes note of the existing theory, and processes, for error correction in such a regime.
As is well know by practitioners of the arts of designing and using error correction codes (ECC), optimal ECC""s for any particular application are a function of many variables including the data block size for which errors must be corrected, the error rate, the correlations in space and/or time (if any) between errors, and the reliability with which error-free data must be reconstituted. The present invention will be seen, in various of its preferred embodiments, to radiatively write, and read, a great number of voxels storing binary bits at one time and in parallel. Although the signal to noise ratio for these operations is excellent, the possibility of error due to many causes in both the media and the media reading and writing system always exists, and ECC""s are commonly employed.
Luckily, a great deal is known about correcting errors in optically stored information. See, for example, the following references:
S. A. Dombrovski, xe2x80x9cEffectiveness of using error-correcting codes in holographic storage systems,xe2x80x9d Optoelectron. Instrumen., Vol. 2, pp. 58-62, 1989.
B. J. Goertzen and P. A. Mitkas, xe2x80x9cError-correcting code for volume holographic storage of a relational database,xe2x80x9d Optics Letters, Vol. 20, No. 15, pp. 1655-7, Aug. 1, 1995.
M. A. Neifeld and J. D. Hayes, xe2x80x9cError-correction schemes for volume optical memories,xe2x80x9d Applied Optics, Vol. 34, No. 35, pp. 8183-90, Dec. 10, 1995.
M. A. Neifeld and J. D. Hayes, xe2x80x9cParallel error correction for optical memories,xe2x80x9d Optical Memory and Neural Networks, Vol. 3, No. 2, pp. 87-98, 1994.
B. H. Olson and S. C. Esener, xe2x80x9cPartial response precoding for parallel-readout memories,xe2x80x9d Optical Letters, Vol. 19, No. 4, pp. 661-3, May 1, 1994.
Wei-Feng Hsu and Alexander A. Sawchuk, xe2x80x9cImproved Usable Capacity for Optical Page-Oriented Memories with Smart Pixel Interfaces,xe2x80x9d International Symposium on Optical Memory and Optical Data Storage, Optical Society of America, Maui, Hi., Jul. 8-12, 1996.
Wei-Feng Hsu and Alexander A. Sawchuk, xe2x80x9cDesign of Smart Pixel Interfaces for Volume Optical Memories,xe2x80x9d Proc. 1996 International Topical Meeting on Optical Computing, OC ""96, Sendai, Japan, Apr. 21-25, 1996.
Steve Blair and Kelvin Wagner, xe2x80x9cInverse filtering during recording for page-oriented optical storage,xe2x80x9d Optical Processing and Computing, SPIE""s International Technical Working Group Newsletter), pp. 3,4,12, October 1997.
T. Maeda, H. Sugiyama, A. Saitou, K. Wakabayashi, H. Miyamoto, and H. Awan, xe2x80x9cHigh-Density Recording by Two-Dimensional Signal Processing,xe2x80x9d SPIE, vol. 2514, pp. 70-72.
Sieji Kobayashi, Toshihiro Horigome, Joost P. de Kock, Hisayuki Yamatsu, and Hiroshi Ooki, xe2x80x9cSingle carrier independent pit edge recording,xe2x80x9d SPIE, vol. 2514, pp. 73-81.
Jeffrey Zarnowski and Matt Pace, xe2x80x9cImaging options expand with CMOS technology,xe2x80x9d Laser Focus World, pp. 125-130, June 1997.
Generally, (i) the detection of optically-recorded data can be quite sophisticated, and (ii) electronic computational parallelism can be invoked for the high-data-rate post-detection correction of errors occurring in two-dimensional, or bit plane, optically-detected data. In combination, state-of-the-art (i) optical detection and (ii) error correction are not presently believed to any substantial hindrance to realization of certain optical memories of the present invention which, in their more extreme forms with data transfer rates on the order of 1 terabits/second (1 terabit, or 1xc3x971012 bits, per second), are faster than any other form of digital memory heretofore realized.
2.6 Particular Prior Artxe2x80x94Doubly-telecentric Afocal Lenses
The present invention will be seen to use a doubly-telecentric lens-based afocal imaging system. Although, to the best knowledge of the inventor, doubly-telecentric afocal lenses have not heretofore been used in conjunction with optical memories and/or optical recording, the optical properties of the doubly-telecentric afocal lens configuration are known, and these lenses have previously been used in optical distance measurement.
For example, U.S. Pat. No. 5,708,532 for a DOUBLE-SIDED TELECENTRIC MEASUREMENT OBJECTIVE to Wartmann assigned to Jos. Schneider Optische Werke Kreuznach GmbH and Co. KG (Kreuznach, DE) concerns a double sided telecentic measurement objective for contactless length measurement in two-dimensional and three-dimensional space. The objective has an image-side optical system consisting of three elements equivalent to those of an object-side optical system but in the reverse order, including a cemented positively refracting lens element turned toward the object of image respectively, a collecting lens spaced by an air gap from the cemented lens, and a dispersive meniscus spaced by an air gap from the collecting lens. The widths of the air gaps between the collecting lenses and the meniscus are substantially greater than the widths of air gaps between the cemented lens elements and the collecting lenses.
The present invention contemplates devices, methods, imaging systems and optical media serving to optically record (write), and read, digital data (i) at massive parallelism (ii) within the three-dimensional volume of an optical mediumxe2x80x94preferably a rotating optical disk made of inexpensive polymer plastic containing an photoactive chemical (a xe2x80x9cphotochemicalxe2x80x9d)xe2x80x94by use of (iii) a depth-transfer optical (lens-based) read/write head, particularly of the doubly-telecentric afocal type.
The preferred embodiment of the invention is thus a three-dimensional (xe2x80x9c3-Dxe2x80x9d) optical disk systemxe2x80x94similar to the optical disks known as the Compact Disk (xe2x80x9cCDxe2x80x9d) or the Digital Video/Versatile Disk (xe2x80x9cDVDxe2x80x9d)xe2x80x94or a xe2x80x9c3-D CDxe2x80x9d system for short.
The recording, or writing process is preferably, but not invariably, by a two-photon (i.e., a two-beam) optical, also known as a radiation, process (xe2x80x9c2-Pxe2x80x9d). The reading process is preferably a one-photon (i.e., a single-beam) optical, or radiation, process (xe2x80x9c1-Pxe2x80x9d). The preferred embodiment of the invention may thus be concisely referred to as a xe2x80x9c2-P writexe2x80x9d, and a xe2x80x9c1-P readxe2x80x9d, 3-D CD optical, or radiation, memory.
1. Immediate Background to the Invention: Photochemicals and Two-Photon Absorption
The primary aspect of the present invention is a Depth-Transfer Optical (xe2x80x9cDTOxe2x80x9d), lens-based, read/write head, particularly of the doubly-telecentric afocal type, and the volume radiation, or optical memory (especially as may be of the 2-P write 1-P read 3-D CD type) that may be written and read (at massive parallelism) by use of such a read/write head.
However, it is useful to understand exactly what photosensitive medium is being radiatively written and read, and how it is so written and read, before the new doubly-telecentric afocal lens read/write head of the present invention is discussed. Accordingly, certain preferred storage media of the volume radiation, or optical, memory of the present invention are first discussed in this section.
The memory of the present invention, including in its preferred 3-D CD form, may be implemented so as to be fully readable, writeable, erasable and rewriteable. If so implemented then the preferred photochemical of the memory is spirobenzopyran. Spirobenzopyran is a known photochemical the use of which in optical memories is taught in, for example, in prior U.S. Pat. No. 5,325,324 for a THREE-DIMENSIONAL OPTICAL MEMORY. If so implemented then reliable permanent storage in the memory can only be realized when the memory is written, read, and maintained at considerably colder than room temperature, preferably much less than 0xc2x0 C.
Instead of being implemented as a read-write-erasable memory, the preferred 3-D CD memory of the present invention is strongly preferably implemented as a memory of the read-once, write-many, or WORM, type. In this realm the preferred 3-D CD memory of the present invention is fully operative for reading, writing and long term stable information storage entirely at room temperature (although undue exposure to strong extraneous light radiation is to be avoided in a similar manner that magnetic disks are preferably not exposed to strong magnetic fields).
The preferred 3-D CD memory of the present invention is so preferably implemented as a memory of the xe2x80x9cWrite Once, Read Manyxe2x80x9d or xe2x80x9cWORMxe2x80x9d, type by the use of a novel writing method employing new photochemicals. (This method and these new photochemicals are the invention of others, and, although taught within the present specification disclosure, are not the subject of the present invention.) In the new methods (i) dye precursor molecules that are reactive with at least one of acids, bases, ions or radicals to produce dye molecules having differing spectroscopic properties than do the dye precursor molecules, are placed within a same volume along with (ii) light-sensitive molecules that, when exposed to light, undergo photochemical reaction so as to form at least one of the acids, bases, ions or radicals with which the dye precursor molecules are reactive. In use as an optical memory, the dye precursor molecules are so reacted with at least one acid, base, ion or radical that is photo-generated from the light-sensitive molecules by, and in the presence of, light radiation, thereby to form the dye molecules. In simplest terms, a photochemically-induced change at and in an illuminated domain, or voxel, is causing a localized chemical reaction in the domain, or voxel, that, ultimately, produces a stable dye. The stable dye is produced at, and only at, those domains, or voxels, that are properly radiatively illuminated.
The dye precursor molecules preferably consist essentially of rhodamine B, and are more particularly rhodamine 700 laser dye reacted with potassium hydroxide. The light-sensitive molecules preferably consist essentially of aromatic ortho-nitro-aldehyde compounds as acid photo generators, and more particularly o-nitro-benzaldehyde or, most preferably, 1-nitro-2-naphaledehydexe2x80x94both of which photochemicals undergo, upon excitation with ultraviolet light, phototransformation into nitroso acid.
In operation of the optical memory the dye precursor moleculesxe2x80x94normally rhodamine basexe2x80x94which are held in a transparent matrix are reactive with acids, bases, ions or radicalsxe2x80x94and in the case of rhodamine are reactive with acidsxe2x80x94to produce dye moleculesxe2x80x94i.e., rhodaminexe2x80x94having markedly different spectroscopic properties. The light-sensitive moleculesxe2x80x94namely, the compound of ortho-nitro-aldehyde, in particular o-nitro-benzaldehyde or, preferably, 1-nitro-2-naphaledehydexe2x80x94in the same matrix undergo photochemical reaction when selectively exposed to light so as to form at least one of the acids, bases, ions or radicals with which the dye precursor molecules are reactivexe2x80x94preferably nitroso acid. The chemical reaction of rhodamine base dye precursor molecules with photochemically produced nitroso acid within those domains that are radiatively-selected two-dimensionally, or within those voxels that are radiatively-selected three-dimensionally, by a first-frequency xe2x80x9cwritexe2x80x9d radiationxe2x80x94particularly including such a xe2x80x9cwritexe2x80x9d radiation as may be realized by two-photon absorptionxe2x80x94produces stable rhodamine dye in the radiatively-selected domains/voxels. Subsequent illumination with a single second-frequency xe2x80x9creadxe2x80x9d radiation induces strong fluorescence in the dye of the written domains/voxels while leaving all chemicals/photochemicals unchanged. (The color of the dye, which goes to its index or refraction and radiation attenuation properties, is also strongly detectable. However, it is preferred to detect the read-radiation-induced flurescence.) The induced fluorescence may be imaged to a detector, such as a charge coupled device (CCD), to reliably realize a high signal-to-noise, non-degrading, radiation, or optical, memory. In accordance with the fact that the stable dye of each domain/voxel is created just once by an irreversible process, the radiation, or optical, memory is of write once, read many (WORM) type.
Neither this new combination of photochemistry and chemistry, nor this (it is believed) new type of optical memory store so realized by use of new photochemicals, are the subject of the present invention. That is, the (believed) new type of photochemical/chemical optical memory, and the (believed) new photochemicals for use in optical storage, are the inventions of persons other than the inventor of the present invention. This other invention is presently assigned to an assigneexe2x80x94The Regents of the University of Californiaxe2x80x94other than the assignee of the present invention. However, none of this (believed) new approach has been publicly disclosed as of the date of the filing of this application. Accordingly, it is now disclosed, with permission, within this specification in support of the best mode of implementing his invention of which the inventor of the present invention is aware.
When so implemented as a photochemical/chemical process WORM memory, the preferred 3-D CD of the present invention is fully reliably operable for writing, reading and storing data entirely at room temperature, and is completely stable during all other normal environmental variationsxe2x80x94although excessive heat and prolonged exposure to bright light are to be eschewed. Indeed, rhodamine is well known as a stable dye which fluoresces brightly over many cycles.
It will be understood by a practitioner of photochemistry, and of the design of photochemically-based optical memories, that photochemicals are still under intense widespread active development worldwide, and that the (primarily optical) principles of the present invention taught herein are fully applicable to optical media incorporating new and improved photochemicals as such becomes available in the future.
Just as photochemicals are not the basis of the present invention, neither are photonic processes, particularly including multi-photon, and still more particularly two-photon, processes. However, it is again useful to understand how, when and why an optical memory store must be radiatively illuminated for both reading and writing before proceeding to consider how the depth-transfer, doubly-telecentric afocal lens, read/write head of the present invention accomplishes this reading and writing at massive parallelism.
Two-photon (xe2x80x9c2-Pxe2x80x9d) processes for the radiation reading and writing of information transpirexe2x80x94for those totally unfamiliar with the conceptxe2x80x94as follows: The preferred 2-P writing changes the state of a photochemicalxe2x80x94more particularly the preferred nitro-naphthaldehyde is changed to nitroso acid, or, alternatively, spirobenzopyran is changed in isomeric molecular formxe2x80x94at selected voxels, located within the 3-D volume of the optical disk, where, and only where, the two radiation (light) beams are spatially and temporally coincident. Reading may thereafter traspire by either a 2-P or a 1-P process.
In 1-P readingxe2x80x94which will be found to be the preferred method of radiatively reading in the present inventionxe2x80x94a single beam of radiation (e.g., light, and more commonly laser light) is used to illuminate a large number of voxels in common. Voxels containing chemicals that are in a one state (e.g., that have been (i) converted to rhodamine dye by chemical reaction with the nitroso acid, or that are (ii) at have assume their second, merocyanine, isomeric molecular form in the case of spirobenzopyran) produce a different response(s) to the illuminating radiation than those that are within the complimentary state (e.g., that still exist as (i) rhodamine base, or that remain in (ii) the spiropyran isomeric molecular form of spirobenzopyran). For example, the preferred phtochemicals (rhodamine base/rhodamine, or, alternatively, merocyanine/spiropyran) differ in greatly between their two states in both their (i) opacity/transmissivity and their (ii) fluorescent emission. Either of these differing responses can be used as the basis of detection of the written versus the unwritten forms. However, the bright fluorescent emissions (especially in the case of the xe2x80x9cwrittenxe2x80x9d rhodamine dye) of the illuminated voxels are preferably imaged to a detector as an indication of the binary information previously radiatively stored within the voxels.
The radiation readout is substantially non-destructivexe2x80x94particularly for rhodamine dye. For a reversible photochemicalxe2x80x94namely, spirobenzopyranxe2x80x94the written voxels may be radiatively written, including to the opposite state (i.e., erased), and re-written, read and re-read, indefinitely many times and, depending upon any fatigue of the particular photochemical(s) involved, typically thousands or tens or hundreds of thousands of times. It will be recognized by photochemists that some photochemicals such as bacteriarhodopsin have a higher operating temperature than does spirobenzopyran, but are more subject to fatigue after several tens or hundreds of erase and/or re-write cycles.
2. Theory, and Advantages, of the Present Invention
Some background to the photochemistry and chemistry of two preferred optical memory storesxe2x80x94one of which is believed to be wholly newxe2x80x94and the general requirements of their radiation(s) illumination(s) now having been discussed, explanation of the present invention now commences.
The present invention addresses a paramount challenge in building a radiation (i.e., optical) memory: how to reliably repeatedly efficiently effectively quickly acquire and image multiple voxels, especially as may be located within volumes, for radiation reading and writing. The present invention is based on the realization that a great number of information-containing voxelsxe2x80x94each containing typically one and possibly even more bits (of differing xe2x80x9ccolorsxe2x80x9d)xe2x80x94within each of a large number of plane segments located within the volume of an optical medium, normally an optical disk, may be imaged at (typically) massive parallelism when these imaged plane segments within the medium are tilted (i.e., angled) relative to external major planar surfaces of the optical medium (e.g., to the major planar surfaces of the optical disk).
This bears repeating: the present invention contemplates reading and writing bit planes that are tilted relative to major planar surfaces of the medium, preferably and by example the medium of an optical disk. The optical mechanism that accomplishes thisxe2x80x94a read/write head that reads bits in and from planes that are tilted relative to, for example, the major planar surfaces of the preferred optical disk configuration and that are within the optical diskxe2x80x94is a most important part of the present invention. This new read-write head incorporates a xe2x80x9cdepth transfer objectivexe2x80x9d or xe2x80x9cDTOxe2x80x9d; more specifically and most preferably a DTO in the form of a doubly-telecentric afocal lens.
For example, the DTO of the present invention will support, by way of illustration and not by way of limitation, that some 128xc3x97128 bits (i.e., 16,384 bits) may be located in each of a very great number of tilted bit plane segments that are themselves located within the volume of, and in xe2x80x9csupertracksxe2x80x9d distributed annually around the circumference of, a three-dimensional optical disk, or 3-D CD. When written or read by the preferred doubly-telecentric afocal lens read/write head of the present invention, all of the bits within a single bit plane segmentxe2x80x94i.e., the 16,384 bitsxe2x80x94are imaged in common at the same time.
Moreover, by moving the optical medium transvesely relative to an optical read axis, successive tilted bit plane segments may be successively written, or read. Normally the optical read axis and the read/write head of the present invention remain, at least momentarily for some milliseconds or seconds, stationary in the world""s reference frame while an optical disk containing the bit planes is spun underneath the read/write head. For the particular optical medium of an optical disk the tilted bit plane segments internal to the medium (the disk) collectively have the rough appearance of the angled blades of a fan, or, more precisely, a turbofan. The tilted bit plane segments are closely packed: one segment overlapping another in directions orthogonal to the major surfaces of the disk.
In accordance with the present invention, all the great many binary data bits (e.g., from 16,384 up to 106+) as are associated a correspondingly great number of physical domains, or voxels, (e.g., from 16,384 up to 106+voxels) located within each of a great many tilted data (or bit) plane segments (e.g., from 5xc3x97109 up to 1010 such segments) internal to the optical medium are efficiently effectively reliably simultaneously imaged by the special (i) Depth Transfer Objective (xe2x80x9cDTOxe2x80x9d) optics (ii) present within a passive optical read/write head (iii) to a conjugate image plane that is located in free space outside the outside medium.
The DTO optics preferably consist of a doubly-telecentric afocal lens-based imaging system, which system itself preferably consists of but two complimentary convex lenses (i.e., the simplest type of doubly-telecentric afocal lens system). xe2x80x9cDoubly-telecentricxe2x80x9d means that the imaging system is telecentric in both (i) the object space and (ii) the image space.
This doubly-telecentric afocal lens system is the basis of a read/write head which, in its location above one major surface of the disk, may be completely passive, and need not ever move at all as the disk spins beneath it. (The optical path through the preferred two complimentary convenx lens that form the preferred doubly-telecentric afocal lens system may be folded by use of a simple mirror, in which case the mirror also becomes part of the optical path of the read/write head.) A read/write head that is unmoving nonetheless serves to image many successive tilted bit plane segments that are within the disk rotating beneath the head, thereby radiatively reading, or writing, an annular band - - - called a xe2x80x9csupertrackxe2x80x9d - - - of a portion - - - called a xe2x80x9csuperlayerxe2x80x9d - - - of the entire thickness of the disk. The width of the imaged annular ring, or supertrack, is not normally so wide as is the usable annular area/volume of the entire disk and is, indeed, typically but a small fraction, typically on the order of less than {fraction (1/39)}, of the width of the annulus. Accordingly, even should a number of annular xe2x80x9csupertracksxe2x80x9d, say 39 such xe2x80x9csupertracksxe2x80x9d be present upon the 3-D CD, there will remain unused regions to the interior, and to the exterior, of the annulus of the disk - - - as is conventional.
Similarly, each imaged thickness, or superlayer, is normally much much thinner than is the thickness of the entire disk and is, indeed, typically but a small fraction, say less than {fraction (1/45)}, of this thickness. Accordingly, even should a number of xe2x80x9csuperlayersxe2x80x9d, say 45 such xe2x80x9csuperlayersxe2x80x9d be centrally located within a 3-D CD, there will remain unused, unwritten and unread buffer layers at the very top, and at the very bottom, surfaces of the disk. This is distinctly oppositely to present optical disks where these surfaces are the very ones used! Clearly the read-write head, and method, of the present invention makes use of the interior volume of an optical medium, including most particularly an optical medium in the form of an optical disk.
The read/write head of the present invention may, and preferably does, move under servo control. It preferably moves transversely radially to the rotating disk in a conventional manner so that different circumferential supertracks (similar to tracks of conventional optical disks) may be sucessively accessed. The read/write head may either assume a modest number, say 39, discrete radial positions across the annulus of the disk, or it may trace a continuous spiral on the disk - - - both of which access patterns and associated servo control are just like those for existing (single bit) optical read/write heads. However, and unlike the servo control of present read/write heads, the read/write head of the present invention may additionally emply servo control of, say, xc2x11xc2x0 in its tangential angel - - - but this is not invariably required. This servo control (i) in radial position and, optionally additionally, (ii) in tangential angle, is useful to accurately image the bit planes that are within any one supertrack.
Also unlike conventional servo control of read/write heads of presently existing optical disks, the read/write head of the present invention is preferably adjustable (in steps) to greater and lessor distance of separation from the surface of the optical disk, thereby to permit the imaging of multiple sucessive superlayers within the volume of the disk. This movement to greater and lessor proximity from the optical disk is not to be confused with the fact that a read head that is fixed in position of separation from the disk may read (or write) all the bits that are within the entire depth of all the tilted bit planes that are within the particular superlayers that is imaged. Typically some 45 superlayers, with a thin buffer zone between each superlayer, may be imaged, one superlayer layer at a time, by movement of the read/write head to some 45 corresponding xe2x80x9cz axisxe2x80x9d positions.
Clearly the volume of the disk, or any other optical media, can be xe2x80x9csplit upxe2x80x9d into other and various numbers and forms of xe2x80x9csupertracksxe2x80x9d and xe2x80x9csuperlayersxe2x80x9d and not just, for example, 39 supertracks in each of 45 superlayers (or, conversely, 45 superlayers in each of 38 supertracks). The present and ensuing explanation of the present invention covers possible movement of the read/write head of the invention in all three possible axis (xe2x80x9cxxe2x80x9d, xe2x80x9cyxe2x80x9d, and xe2x80x9czxe2x80x9d), and also in one angle (xe2x80x9cxcexdxe2x80x9d), substantially only so that it may be shown how simple these movements are, and how all such movements may be quite readily accomplished totally without any improvements in the accuracies, response times, or any other characteristics of servo system and servo control loop technologies already existing.
In other words, servo positioning of the read/write head of the present invention (which, it is emphasized, need not ever be servo positioned in any manner whatsoever in order to read astounding amounts of stored data) is merely expanded in the number of axis, and in one angle, in which position, and angle, are controlled, with all such servo positioning being conventionally realized.
Being that the optical read/write head of the present invention is preferably and easily moved in position (and, indeed, is so moved in one more dimension - - - z - - - than is conventional) it might be wondered why the fifth preceding, and the immediately preceding, paragraphs paused on the degenerate case of where there is no read/write head movement at all. This was because even this trivial case, which is extremely inexpensive to implement, retrieves usefully copious amounts of digital data. For example, several million bits may be stored in but {fraction (1/39)} of the annulus (i.e., one supertrack), and in but {fraction (1/45)} of the thickness (i.e., one superlayer), of a 2.54 centimeter (one inch) diameter 10 mm thickness optical disk.
Moreover, it will later be explained that (i) the optics of the read write head, and of some (ii) addressing beam-forming optics, all require only rough (fractional millimeter as opposed to micrometer) accuracy in their positional placement relative to the optical disk media. The component placement accuracy desired in implementation of the optical system of the present invention is more characteristic of a plastic than of a metal fixture. Therefore, and nonetheless to its prodigious data storage capacity, an optical disk system in accordance with the present invention should be thought of as being usefully built from plastic more along the lines of existing mass-market phonorecord and compact disk players than - - - despite the possible use of multi-axial servo control - - - from machined metal as would be characteristic of a Winchester magnetic disk.
Neither are the preferred lenses of the optical disk system, although preferably of optical quality, particularly precise or expensive. Admitedly, excessive wow, wobble or flutter cannot be tolerated in the optical disks and disk drive, although this normally presents no special challenge because the drive and its spindle and the optical disks are manufactured round. Permissible variations in the rotational speed of the optical disk are much broader than those normally encountered, and such variations as do occur are readily encompassed by encoding the read clock in the read data. (The write clock is normally controlled from a conventional crystal oscillator).
The detector array for the system of the present invention is not yet commercially available in the most preferred technology (active pixel sensors) at the most preferred sizes (about 4 cm2) having highest sensitivity at the most-preferred light wavelengths (500-1000 nm). However, existing simple, inexpensive and readily available arrays of Charge Coupled Devices (CCDs) serve adequately as detectors.
Read illumination is preferably accomplished by inexpensive laser diodes. Write illumination (for units that write) is somewhat more expensive, requiring a low power laser.
Therefore, and although the preferred photochemistry/chemistry of the memory store might be considered sophisticated, no optical nor disk drive system components, nor any system control, hereinafter discussed should be though or suspected to be any more complex than will be candidly admitted. Instead, an optical engineer will come to recognize that most, if not all, of the optical disk system of the present invention may be tolerably implemented with only such accuracies (as must ultimately suffice to read and write a bit domain of a chosen size and volume), and with only such components, as are quite generally and readily, and even easily, obtainable. In this manner the present invention is hopefully somewhat different from the optical memories of the prior art that, while often projecting prodigious storage capacities, have often seemed to fail to teach an apparatus that is practically, or at least econmically, realizable.
Returning to the imaging performed by the read/write head of the present invention (whether, and wheresover, moved in three-dimensional spatial position, and also in angle tangential to the supertrack), the conjugate image plane imaged by the read/write head is, just like the data plane segment, tilted. In its position outside the disk this conjugate image plane is, in fact, angled complimentary to the data plane segment that is within the volume of the optical medium. In other words, the image plane located in free space on one side of the DTO optics is conjugate, and complimentary, to the data plane segment that is embedded within the optical medium on the other side of the DTO optics. An optical sensor array may be, and most often is, located directly in the conjugate image plane.
Because the optical path of the image may readily be variously folded and directed, with the image being rotated or expanded or compacted - - - all in accordance with the principles of optics - - - as is desired, the optical path of the image preferably is so folded for ease of component location and access, and for compactness of packaging. In a most preferred configuration of the 3-D CD, after the image (of an entire tilted data plane segment within the volume of the disk) passes though a first convex lens of the preferred doubly-telecentric afocal imaging system, this image impinges upon a simple plane mirror set at a 45xc2x0 angle, and is then re-directed parallel to the disk. The re-directed image then passes (i) through the second convex lens of the preferred doubly-telecentric afocal imaging system and (ii) onto an optical sensor array located in the angled conjugate plane. This sensor array is thus, nonetheless its location, still at the optical location of the conjugate image plane. The sensor array - - - which deals with the image in the conjugate image plane - - - takes the form of (i) an array of selectively masked optical emitters for writing the optical disk, or (ii) an optical detector array for reading the optical disk.
Imaging of successive internal data plane segments within a rotating optical disk is totally without large-stroke physical motion, nor any need to reacquire tracking, focus or synchronization. Acquisition of all the data from all the pixels, or voxels, located in each (tilted) data plane segment is simultaneous, and in parallel. As stated, the xe2x80x9cparallelxe2x80x9d optical readout head is preferably controllable to move radially across the annulus of the spinning optical disk in a conventional manner. It may so move between successive concentric circular tracks, as is typical of a magnetic Winchester disk, making that the data within the optical disk will then be read out at constant angular velocity (CAV). Alternatively, it may so move in a spiral track at a constant linear velocity (CLV), as is typical of an conventional Compact Disk (CD). Finally, it may so move between successive spiral track segments in a zoned constant angular velocity (ZCAV) - - - which is another contemporary, but little-used, standard for CD""s.
It should be noted that the existing, prior art, standard for DVD""s incorporates each of CAV, CLV and ZCAV - - - although it is uncertain that any one DVD player-recorder will function in multiple formats. The 3-D CD system of the present invention can work with any, and all, of the CAV, CLV and ZCAV formats. Indeed, because the optical readout head of the present invention need generally be moved no faster, nor any more uniformly, nor any more accurately - - - and possibly not even so precisely if correction of any mis-registration to the supertrack is performed electronically - - - than is typically presently required in order to track a single xe2x80x9clinexe2x80x9d of bits. A single 3-D CD unit of the present invention is able, under appropriate electronic control, to variously read and write in a manner similar to any of CAV, CLV and ZCAV - - - each of which standards has strengths for certain applications.
Moreover, at least the prior art method of CAV suffers in that the size of the domains in which data is impressed are larger at the periphery of the disk, and smaller near its central annulus. The 3-D CD of the present invention optionally preferably employs multiple xe2x80x9csupertracksxe2x80x9d. (Multiple supertracks are xe2x80x9coptionalxe2x80x9d only because it is possible to implement an optical disk having a quite impressive storage capacity with but one only supertrack). One supertrack at a time is imaged by moving with under servo control the optical read/write head, and the Depth Transfer Objective (DTO) optics of the read/write head, into position over the supertrack. The xe2x80x9csupertracksxe2x80x9d readily permit that the tilted bit planes located in a circumferential band at the periphery of the disk are commensurately greater in number than are the number of tilted bit planes within an a interior annular band. For example, consider if each bit plane is xe2x80x9cscannedxe2x80x9d or xe2x80x9cdetectedxe2x80x9d at an approximately equal rate - - - meaning that it was originally written in accordance with a standard clock and that it is subsequently read at rates as may be determined by a Manchester-type code present within the stored data. Clearly there will be more bit planes in the outer supertracks, and fewer bit planes in the inner supertracks. Accordingly, not only is the substantial annular volume of the optical disk filled with data, it is so filled at substantially the same (high) density.
Moreover, there may be, and preferably are, multiple vertical layers - - - superlayers - - - within a single disk. Access to each superlayer, and to all the supertracks of the layer, occurs by servo-positioning the optical read/write head, and the Depth Transfer Objective (DTO) optics that comprise the head, to a greater or a lessor separation from the disk. At least one, and sometimes two, illuminating beams as may in part pass through optics other than the read/write head are necessary to read and to write the disk. These beams may also be adjusted in position by servos - - - but this is not normally necessary if each of the beam positions, angles and dispersions are carefully considered! In two different orientations of these read/write beams that are called xe2x80x9cco-linearxe2x80x9d and xe2x80x9cconfocal-thetaxe2x80x9d one beam - - - the sole and only illuminating beam needed to read the disk - - - will be seen to track with the read/write head, and will thus always be accurately positioned. In a final, third, read/write beam orientation called xe2x80x9corthogonalxe2x80x9d, a one illuminating beam illuminates the bit plane through the edge of the (rotating) disk, and again need not be moved in position.
The (i) entire general concept of moving optical elements by use of servo motors, and more particulary (ii) the moving of an optical read/write head to selected tracks, and, less commonly, to selected separation from the optical disk, is readily, and routinely, implementable. It needs only be considered in assessing the present invention as to whether the servoed motions required are required to be more accurate, or over a wider range, or faster, or more frequent, etc., than heretofore. In other words, the claimed performance of the present invention (hereinafter set forth) should not be surreptitiously dependent upon some futuristic servo and/or servo control technology unless this dependence is specifically acknowledge, and unless this new and superior servo control technology explicitly taught.
In fact, the present invention works quite well with existing servo, and servo control, technologies, and is not particularly demanding of either. In fact, the present invention is arguably very xe2x80x9ceasyxe2x80x9d on required servo technology, and on the required servoed movement of the read/write head. This is because every location of the read/write head brings in some large multiple more information - - - typically thousands of times more information for each (super) track position by millions of times more information for such a fractional millimeter repositioning in the z axis as permits an entire new superlayer to be accessed - - - than heretofore. Commensurately with the vast amount of data recoverable from each supertrack, and each superlayer, the read/write head is typically moved more infrequently, and more leisurely. Finally, the preferred optics of the invention are preferably of such long focal length, and preferably correct for diffraction, so as to commensurately ease the required exactitude of read/write head positioning.
Furthermore, if several terabits of information storage per 13.3 cm (5xc2xc inch) disk (hereafter discussed) proves insufficient, then one possible route for improving the present invention until information should ultimately be stored in domains/voxels the size/volume of a few molecules already exists. Namely, the present invention holds the future promise of permitting focusing, deskewing, tracking, and/or error-correcting by electronic and/or holographic image recognition and renormalization. When you must access one small bit domain at a time, as with present optical disks, then it absolutely must be done accurately. If the bit is xe2x80x9cmissedxe2x80x9d, then no data at all is recovered. This accuracy requirement typically consumes about one-half the total usable area of a conventional optical disk. However, if you can access a million bits at a time as with the present invention, not only do the densities and data transfer rates, and the efficiencies of data storage and retrieval, increase greatly, but so do the efficiencies of error correction. It is impossible to error correct one bit when one bit is read; it is not so hard to error correct a million bits when a million bits are read. This relationship has been poorly understood because, until the present invention, optical parallel data storage systems have not realized such commanding performance as has previously caused all aspects of their performance to be critically regarded. The performance aspects of the present invention will be discussed further at a later point in this specification.
In the meanwhile, it should be considered that the 3-D CD system of the present invention where a single optical read/write head typically reads (i) many xe2x80x9cbandsxe2x80x9d or xe2x80x9ctracksxe2x80x9d wide (i.e., xe2x80x9csupertracksxe2x80x9d) and (ii) many xe2x80x9clayersxe2x80x9d deep (i.e., xe2x80x9csuperlayersxe2x80x9d) not only usefully retrieves great amounts of information per unit time (see section 6. below), but exhibits xe2x80x9clow focal latencyxe2x80x9d. Even when the read/write head can move in one or, as is both typical and preferred, in two axis (i.e., both radially across the disk, and in separation therefrom), it often need not so move in order to access all the data which many computer applications require! In other words, although computer programs have managed to balloon from a few kilobytes to multiple megabyte size in but a few short decades, and although speech and video processing requirements still loom large on the computing horizon, there is some question whether programs, especially for personal computers, can continue present growth rates and balloon to multiple hundreds and thousands of megabytes (gigabytes) in size without employing a substantial portion of the earth""s population as programmers. Accordingly, if one xe2x80x9csupertrackxe2x80x9d of a 3-D CD of the present invention is capable of storing several gigabits of read/writeable information (which it is, see below), then this may be all that is required for one program and its related databases, and the read/write head may not have to move at all for a full day""s computer accesses!.
3. A Depth Transfer Objective Lens Imaging System for an Optical Disk
Therefore, in one of its aspects the present invention is embodied in a head for an optical disk. The head may be a read head, a write head, or, as is preferred, both a read head and a write head.
The head includes a depth transfer objective imaging system. This system images (i) voxels substantially in a plane segment located completely within the medium and tilted relative to the medium""s planar surface to (ii) another, conjugate, plane segment, likewise tilted relative to the medium""s planar surface and located outside of the volume of the medium.
The head is typically used with an optical disk having parallel planar major surfaces, or sides. The depth transfer objective imaging system is preferably a doubly-telecentric afocal lens imaging system. Such an imaging system used with an optical disk serves to image (i) voxels substantially in a plane segment tilted relative to the major planar surfaces of the disk, located along a chord or a radius of the disk and within the volume of the disk, to (ii) another, conjugate, plane segment, likewise tilted relative to the major planar surfaces of the disk, located completely outside of the volume of the disk. The chief rays to all image points are almost parallel to the optical axis (for ideal lenses they are parallel). The imaging system called xe2x80x9cdoubly-telecentricxe2x80x9d because it is telecentric both (i) in an object space and (ii) in an image space. A detector array, onto which images of the voxels are received, may be directly located in the conjugate plane. If so located then it may be about the same physical size as is the imaged plane segment of voxels within the disk, meaning that this plane segment of voxels within the volume of the disk has been imaged by the doubly-telecentric afocal lens imaging system without magnification. Normally in this case the doubly telecentric afocal imaging system is symmetric, with the detector array being located about the same optical distance in one direction along the optical path from the doubly-telecentric afocal lenses as the plane of voxels within the volume of the disk is located in the opposite direction along the optical path. (But, by the principles of optics and of lenses this is not required.)
Alternatively, the detector array may be larger than the plane segment of voxels within the disk. In this case the conjugate plane segment is imaged by the doubly-telecentric afocal lens imaging system at a larger size than is the plane segment of voxels within the volume of the disk; the imaging of the voxels having been with magnification. Normally in this case the detector array is at a greater optical distance along the optical path in one direction from the doubly-telecentric afocal lens imaging system than is the plane segment of voxels within the volume of the disk in the opposite direction along the optical path. Again, however, in accordance with the principles of optics and of lenses, this is not absolutely required.
The detector array in the conjugate plane segment is typically either a charge coupled device or, preferably, an active pixel sensor.
In use of the doubly-telecentric afocal lens imaging system as an optical disk read head a source of illumination for illuminating the voxels within the image plane segment is required. This illumination source can be located an any of at least three separate locations.
The illumination source is preferably located in the plane of the optical disk. It there serves to radiatively illuminate a planar radial cross-section, tilted relative to the plane of the optical disk, across the entire annulus of the optical disk. The illuminated planar radial cross-section contains the plane segment of the imaged voxels. This illumination is called orthogonal because, being in the plane of the disk, it is at a right angle to an optical, imaging, axis of the doubly-telecentric afocal imaging system.
Alternatively, the illumination source may be located to the side of the plane of the optical disk. So located it serves to radiatively illuminate a planar radial cross-section, tilted relative to the plane of the optical disk, containing the plane segment of the voxels. This illumination is called xe2x80x9cconfocal-thetaxe2x80x9d because, being on the side of the plane of the disk as is the doubly-telecentric afocal imaging system, it makes an angle theta with the optical axis of this doubly-telecentric afocal imaging system in a manner similar to confocal-theta microscopy.
Still further alternatively, a source of illumination radiation may be channeled through a beamsplitter in the optical path of the doubly-telecentric afocal imaging system and of the source of illumination radiation, thereby becoming directed onto the plane segment of the imaged voxels. This illumination is called collinear because it is in part along a same optical axis as is the imaging of the doubly-telecentric afocal imaging system.
In each and every case the illumination is sufficient, and sufficiently selective, to cause, of what voxels are within the field of view of the doubly-telecentric afocal imaging system, that all, and only, those voxels that are within the image plane segment will be radiatively illuminated, and will produce a detectable image at the conjugate plane, while all illuminated voxels outside this plane segment (if any are so illuminated) will not be so imaged as anything detectable in the conjugate plane. In other words, although more voxels than those that are within the plane segment may be illuminated, only those voxels that within the plane segment will be imaged to the detector array, and no other illuminated voxels, fluorescent emissions from which might cause optical noise, will be so imaged to the detector array.
When the doubly-telecentric afocal lens imaging system is used as an optical disk write head to write the optical disk then the illuminator is still involved. It is preferably located in the plane of the optical disk - - - the first alternative above. Recall that the illuminator in this location served to radiatively illuminate with a planar radial cross-section, tilted relative to the plane of the optical disk, across the entire annulus of the optical disk. The plane segment of the voxels is a part of this planar radial cross-section. Clearly then this illuminator does nothing as regards selective writing of the voxels by process of two-photon absorption; serving even to illuminate more voxels than are within the place segment. The illuminator in the plane of the optical disk simply supplies one of the two illumination beams required for two-photon absorption.
Meanwhile, a masked second illuminator, located in the conjugate plane, radiatively selectively illuminates with a second frequency radiation through the doubly-telecentric afocal imaging system selective voxels within the plane of voxels. In accordance with the known principles of writing a photochemical medium by process of two-photon absorption, the spatially and temporally coincident illumination with both illumination beams of certain selected voxels with the plane segment (which is tilted relative to the plane of the optical disk and located within the volume of the optical disk) causes a photochemical that is within these selected voxels of this plane segment to undergo a stable change. This stable change is, however, reversible - - - again by two-photon absorption now with the two illumination beams one of which (typically the first illuminator) is now of a different frequency. In other words, the information written by two-photon absorption can be erased by the same means alternatively applied. Importantly, during both two-photon writing and two-photon erasing only the selected voxels, and none are changed elsewhere within the volume of the optical disk.
The same phenomena holds upon reading. Even radiation in the form of fluorescent emissions induced in the photochemical that is within a one state (within such domains as it is in this state) does not combine with the (single) read illumination beam to cause changes anywhere within the optical media.
Accordingly, reading is with one radiation beam. Writing is with two radiation beams. Reading is non-destructive read-out. Importantly, and in accordance with the principles of two-photon absorption, both the reading and the writing processes are very substantially clean, meaning that no appreciable degradation occurs to any voxels during reading, nor to any and all voxels not specifically written during writing.
It might be wondered if the 3-D CD would work - - - at least as a read/writeable memory in not also as a re-readable/re-writeable memory - - - if the writing were not two-photon. For example, might it be possible to perform hole burning or effect other transformations at depth within an optical material! According to the many prior art patents of Swainson, et al. for three-dimensional optical memories, it is so possible. However, as the domains get smaller, and the read/write speeds higher, the xe2x80x9ccleanxe2x80x9d radiation processes of the present invention are highly preferred.
4. A Method of Reading and Writing an Optical Disk with a Doubly-telecentric Afocal Lens Imaging System
In a similar aspect the present invention is also embodied in a method of reading an optical disk.
Voxels within a plane segment of an optical disk, which plane segment is (i) within the volume of the optical disk and (ii) tilted relative to the major planar surfaces of the optical disk, are selectively illuminated.
The illuminated voxels are imaged with a doubly-telecentric afocal lens imaging system (i) the voxels in the plane segment that is tilted relative to the major planar surfaces of the disk being imaged to (ii) another, conjugate, image, plane - - - likewise tilted relative to the major planar surfaces of the disk - - - that is located outside of the volume of the disk.
A detector array is optically communicative with this conjugate image plane. The detector array may simply be located at the conjugate image plane. In accordance with the principles of optics, and of lenses, the detector array may be closer (and smaller) than the conjugate image plane or, more commonly, farther away and larger so as to receive from the doubly-telecentric afocal lens imaging system a magnified image.
The optical path between the imaged plane segment and the conjugate image plane may be folded. It may be so folded by a simple flat mirror located between the two lenses of the doubly telecentric afocal imaging. The mirror serves to reflect the image 45xc2x0 so as to be parallel with the surface of the optical disk and so as to, after passing through the second of the two lenses, intercept the detector array in a conjugate plane that is now located immediately above the disk. The detector array detects the optical properties of the imaged illuminated voxels as an indication of information stored in the voxels.
Typically (but not invariably), the illuminating causes any such ones of the illuminated voxels as are in a particular one of two stable states to fluoresce, and it is this imaged fluorescence that is detected with the detector array as the indication of information stored in the voxels. (Voxels not in this particular one state do not fluoresce when illuminated.)
As with the first aspect of the invention, the illuminating may be (i) orthogonal, (ii) confocal-theta, or (iii) collinear. p The method of writing the optical disk is similar. A planar radial cross-section, tilted relative to the plane of the optical disk and containing a multiplicity of voxels, is radiatively first-illuminated. The first-illumination is normally with first-frequency radiation from a first illumination source.
A masked second illumination source either at, or, more commonly optically transmitted through, the conjugates image plane is further optically communicated through the doubly-telecentric afocal imaging system, therein illuminating selected voxels with within the plane segment. The second illumination, and illumination source, is normally with a second-frequency radiation.
The first-illuminating and the masked second-illuminating serve to jointly radiatively illuminate selected voxels within the plane segment (which is tilted relative to the plane of the optical disk and located within the volume of the optical disk). The spatially and temporally coincident first-frequency and second-frequency radiations are sufficient to; and serve to, stably change a photochemical within the voxels of this segment, and not elsewhere within the volume of the optical disk.
In one, less preferred, embodiment of the invention the photochemical may be radiatively reversed in state; what is written can be oppositely written, or erased. Accordingly, in this embodiment the optical disk is written, re-written and/or erased within its three-dimensional volume only in the locations of the selected voxels, and not elsewhere. Radiative reading is without effect on the written information, or those portions of the memory not yet written.
In another, preferred, embodiment of the invention the photochemical is changed to and acid, and locally undergoes a chemical reaction with a dye precursor chemical to form a dye. This reaction is irreversible, and what is written cannot be oppositely written, or erased. In this embodiment also the optical disk is written within its three-dimensional volume only in the locations of the selected voxels, and not elsewhere. Radiative reading is again without effect on the written information, or those portions of the memory not yet written.
5. A Radiation Memory
In yet another of its aspects the present invention is embodied in a memory system for the parallel writing by process of two-photon radiation absorption, and the parallel reading (with single beam illumination), of data stored in a large number of voxels out of a very large number of voxels all located within the three-dimensional volume of an optical medium, normally an optical disk.
The radiation memory is based on a doubly-telecentric afocal imaging system. As previously explained, xe2x80x9cdoubly-telecentricxe2x80x9d means that the imaging system is telecentric both in an object space and in an image space. The imaging system is adjacent the planar surface of the three-dimensional body so that it serves to image a large number of voxels that are within a plane segment that is both (i) within the body and (ii) tilted relative to the body""s planar surface. These voxels are imaged at a constant magnification over a finite lateral extent across, and throughout a finite depth of, the tilted plane segment within the body. These voxels are so imaged to a conjugate; tilted, image plane segment located outside the three-dimensional body. The voxels contain information susceptible of being sensed by radiation, and the image of the voxels conveys this information.
For writing of the voxels, the system has both first and second sources of radiation illumination. These sources cooperated during writing of the memory store so that (i) the first radiation source first-radiates with a first beam of radiation all the multiplicity of voxels that are within the tilted plane segment meanwhile that (ii) the second radiation source simultaneously second-radiates with a second beam of radiation at least selected ones of the large number of voxels that are within the tilted plane segment. The simultaneous radiation, when and where occurring, changes a photochemical within the selected voxels by process of two-photon absorption.
In one, preferred, embodiment the photochemical (a compound of ortho-nitro-aldehyde) changes into an acid (nitroso acid), which undergoes a chemical reaction with a dye base (rhodamine B) proximately co-located within the matrix so as to turn into a stable dye (rhodamine). In a less preferred embodiment, the photochemical (spirobenzopyran) changes in isomeric molecular form.
Howsoever in detail accomplished - - - and still other mechanization are possible such as those taught within the prior art patents of Swainson, et al. (op. cit.) - - - the optical properties of the selected voxels are changed. (In accordance with the principles of two-photon absorption, voxels not simultaneously radiated by both radiation sources do nothing, and, most important, suffer no change in their optical properties.)
Only one radiation source is required for reading of the optical medium. It is typically one of the two, and more typically the first one of the two, illumination sources that are otherwise used for writing. In other words, writing is with two illumination sources but reading is with but one illumination source. During reading all the voxels that are within the tilted plane are illuminated with (the single beam of illuminating) radiation, causing those selected ones of the voxels previously written (by process of two-photon absorption) to respond in an optically distinguishably different manner than the voxels not so written.
It has been stressed that, in accordance with the selective response of the contained photochemical to illumination radiation, during (two-photon) radiation writing of the optical medium all voxels not radiatively illuminated and/or not in a previously written state do nothing. Most importantly, they do not contribute to noise. So also, it is stressed that no voxels anywhere change their optical properties (as if they were being written, or erased), during the process of (one-photon) reading. This includes the very voxels radiatively read: reading is completely non-destructive.
This is very important. A preferred optical memory in accordance with the present invention does not wear out in the sense that it becomes xe2x80x9cgrayxe2x80x9d. Depending upon the photochemical, the optical memory may be good for only a limited number (typically hundreds or thousands or millions) of write cycles (or of read-write cycles), and the fluorescence from the photochemical may grow dimmer with age, use or high temperature. However, unwritten voxels do not start to assume the properties of the written voxels. Does this make any difference! It is somehow better to degrade by becoming xe2x80x9cdimmerxe2x80x9d as opposed to xe2x80x9cgrayerxe2x80x9d? The answer is xe2x80x9cyesxe2x80x9d. Weak fluorescent emissions can always be compensated for by optical gain, by gain in the optoelectronic detectors, and/or by a longer read dwell time. But when the stored information becomes indistinguishable in its two forms, the memory is worthless. The photochemistry/chemistry of the preferred embodiment memory of the present invention is not presently believed to suffer any such limitations as would affect its use in the tasks to which computer memory stores are normally employed (circa 1998).
During reading a detector array is optically communicative with the conjugate, tilted, image plane. The detector array is most commonly actually located right at, and in, the image plane (in which case the image plane is also the detection plane). In accordance with the principles of optics and of lenses, the detector array may, however, be located closer or further away.
The optical path to the detector array may also include one or more mirrors, or even lenses, in accordance with well-understood optical principles of directing and/or scaling and/or rotating a light beam.
The detector array optically detects - - - all at once and in parallel during reading - - - the optically distinguishably different responses of all the data as is stored in all the voxels within the tilted plane. These responses are, of course, collectively simultaneously imaged to the detector by the doubly-telecentric afocal imaging system. The detected responses are an indication of the data previously written in the voxels that are within the tilted planexe2x80x94which plane is, of course, within the three-dimensional body of, typically, the optical disk.
Accordingly, data is simultaneously written, or read, in parallel from a large number of voxels that are within the three-dimensional volume of an optical body. The data is so read by but one single radiation beam. However, the data is recorded by two radiation beams.
The voxels of the plane segments in which the data is optically addressably recorded within, or read from, one or more photochemicals are defined by the reading, or, more exactly, the writing optics. A virgin volume optical memory is delivered into service as a continuum of photochemical(s) within a stable matrixxe2x80x94meaning that there is no internal metric of any type. The voxels dimensions and voxel locations are subsequently defined by the optics in conjunction with the arrayed encoders and detectors.
Clearly the writing optics write must voxels in three-dimensional positions, if not also of the same size, as may be suitably imaged by the reading optics. Seemingly, given the minute size of the voxels, dimensional registration and alignment would be a great challenge, a challenge at least on the order of a Winchester type magnetic disk. This is not the case. Basically the voxel locations are not highly rigidly definedxe2x80x94not when written, nor relative to one another when read, nor even from time to time as re-written, but are instead relative substantially only to each other.
A remotely analogous concept are the soft sectors, as opposed to hard sectors, of magnetic disks. However, the flexible definition of the soft sectors of a magnetic disk does nothing as regards the (i) data within a sector, nor (ii) the positions of the tracks. Because (i) the optical read/write head takes a large, multi-voxel image off the optical disk (or impresses such an image onto the optical disk), it will be understood that, because the basic spatial relationship between pixels is defined by the write masking and write optics during writing, the written pixels can be quite easily read if any mis-registration in the image(s) can be tolerated.
How big is this xe2x80x9cifxe2x80x9d? It is not very big. If the registration of just three pixel pixels can be located in x, y and z, much in the manner that present optical disks focus in x and y, then this registration can be extended to thousands, and tens and hundreds of thousands, and even millions, of related pixels. (If rotation in the plane is not an issue, as is normal, the position of only two bits need be known!) Moreover, pixels in later-written files need not exactly align with pixels in first-written files if there is some capability, and adequate time, to electronically signal process and interpret collective pixel images that may have slightly different registration.
In accordance with the present invention, there is this capability. It is based on (i) fast optical detectors, such as active pixel sensors or CCD""s, and (ii) fast digital logic that, considerable as the data read rate of the present invention may be, are still capable of timely applying an offset, or a correction, (iii) in accordance with well-established image processing algorithms, to entire xe2x80x9cframesxe2x80x9d of images (which xe2x80x9cframesxe2x80x9d come off the disk in accordance with its rotation rate). In other words, the positional registration of every single voxel image/data bit need not be corrected for nor compensated either (i) mechanically, nor (ii) electronically computationally algorithmically, just entire xe2x80x9cpage imagesxe2x80x9d of, typically, several thousands or tens or hundreds of thousands of data bits at a time.
In section 1 of this SUMMARY OF THE INVENTION section, it was explained that tracking of the optical read/write head was efficient because once the read/write head was properly positioned for one bit at coordinates x,y then it was, proper x-y skew angle being set, at the proper position to read many thousands, or tens and hundreds of thousands of bits. Now it has just been discussed that, if an image can be corrected for three bits than it can typically be efficiently corrected for thousands, or tens and hundreds of thousands, of bits at the same time.
This is exceedingly useful. The (i) rigid positioning, and (ii) error correction, limitations of magnetic, and prior optical, disks are broadly and substantially overcomexe2x80x94even while storage density goes up! This does not mean that the read/write head must not be accurately positioned, and that error correction is unnecessary; it only means that once these functions are performed as currently, and certain slight other factors (related to image angular skew) are taken account of, then large performance gains may be registered with use of what are substantially already existing (i) tracking devices and (ii) error correction methods.
This sounds too good to be true. Certainly an optical read-write head cannot be simply xe2x80x9chung to the sidexe2x80x9d of a rotating disk at current standards of positioning and imaging accuracy and retrieve thousands, and tens and hundreds of thousands, of bits at one time, or can it? It is true in the present inventionxe2x80x94but largely only because dimensional control challenges have been, by subtle design choices, excluded from negatively affecting the z imaging axis. Certain design choices in the preferred 3-D CD optical memory of the present inventionxe2x80x94choices mostly involving the focal lengths of lensesxe2x80x94preclude and exclude that positional control and error correction problems should bedevil the problem of locating the read/write head in the z axis. In other words, in order to read a single xe2x80x9csuperlayerxe2x80x9dxe2x80x94which is often a quite reasonable choicexe2x80x94the read/write head does not require the same control in the z axis that, howsoever conventionally, it requires in the x and the y axis. The z axis servo control system, is still needed, however it may be even less accurate than the x-y servo. Moreover, lack of z axis sensitivity helps to ensure robust and reliable performance of the 3-D CD under shock, vibration and multitudinous other variations, changes and differences. The particular design choices leading to the z-axis insensitivity will be discussed in the DESCRIPTION OF THE PREFERRED EMBODIMENT section of this specification.
Note also that the voxels which are located within the three-dimensional volume of the disk are substantially located in planes that are (i) tilted relative to the major planar surfaces of the disk and (ii) located along a chord or a radium within an annulus of the disk. The collective planes thus have the substantial form of the blades of a turbine or turbofan, or of a gas compressor. This structure therefore leads us to the next section, where it is noted that an written optical disk in accordance with the present invention has a unique form.
6. An Optical Disk
Therefore, in yet another of its aspects the present invention will be recognized to be embodied in an optical disk of particular characteristics. The optical disk is characterized in that information is optically recorded within a chemical or a photochemical within addressable voxels located within the three-dimensional volume of the disk. Moreover, these voxels are located substantially in plane segments that are (i) tilted relative to the major planar surfaces of the disk and (ii) located along a chord or a radius within an annulus of the disk. The collective plane segments have the substantial form of the blades of a turbine. They are overlapping, meaning that an imaginary line through the disk perpendicular to its major surfaces will intersect multiple plane segments.
The chemical or photochemical induced to undergo a stable change, preferably by process of two-photon absorption. Thus information is optically radiatively recorded, preferably by process of two-photon absorption.
Normally the information is optically radiatively recorded at least one particular wavelength, and the addressable voxels are preferably optically defined to be at or near the diffraction-limited spot size relative to this at least one wavelength. In other words, the voxels are exceedingly small. As is also determined by the optics, the voxels exceedingly dense, being separated by a distance on the order of their own dimension.
In order to be so small, the changes radiatively effected in the minute voxels must be strongly readily detectable. The preferred chemicals or photochemicals fluoresce brightly in their written form, and, with the high sensitivity of modern light detectors (which, in forms used in astronomy can detect a single photon), the many molecules that are within a domain of diffraction-limited size, and the corresponding fluorescent emission from these many molecules, more than suffice for adequate signal-to noise for detection.
7. Details of the Preferred Optical Disk Radiation Memory
Therefore, and returning to the radiation memory aspects of the present invention, the present invention will be recognized to be embodied, in the detail of its preferred implementation, in a radiation memory store in the form of an annular optical disk. The disk contains within its volume one or more photochemicals and chemicals suitably written by process of two-photon absorption to change from a first to a second stable state, and suitably read by process of single beam illumination (or by the more complex two-photon absorption!) to produce a different optical output dependent upon which of the two stable states is presently assumed.
During reading, a first illuminator is preferably located in the plane of the optical disk, and serves to radiatively illuminating with a first-frequency radiation of a planar radial cross-section, tilted relative to the plane of the optical disk, across the entire annulus of the optical disk.
A planar matrix of radiation detectors is located to one side of and tilted relative to the plane of the optical disk so as to form a conjugate plane to the illuminated plane segment within the plane of the optical disk. The detectors of this matrix individually detect incident radiation.
A doubly-telecentric afocal imaging system, located on the side of the optical disk between the optical disk and the radiation detectors, images the illuminated plane segment, and the photochemical therein, onto the planar matrix of radiation detectors.
By this coaction the imaging and the matrix of radiation detectors jointly serve to define arrays voxels, meaning volumes of information storage, within the photochemical that is within the illuminated plane segment that is within the volume of the optical disk. (This photochemical within the volume of the disk is as a continuum without distinction or differentiation or boundary at times before the optical disk is first written.)
An electronic signal processing and data recovery means interprets the incident radiation individually detected at all the matrix of radiation detectors as being the binary data content of the arrayed voxels of such plane segment of the disk as has been radiatively illuminated by process of two-photo absorption.
A motor serves to rotate the optical disk relative to the first illuminator, the second illuminator, the planar matrix of radiation detectors, and the doubly-telecentric afocal imaging system so that successive volumes of the optical disk, and of its photochemical(s) and/or chemical(s), serve as the illuminated plane segment, making that binary data content may be radiatively read from a 360xc2x0 annular ring, or band, or xe2x80x9csupertrackxe2x80x9d, of the optical disk.
A optional tracking means serves to move the second illuminator, the planar matrix of radiation detectors, and the doubly-telecentric afocal imaging system radially across the rotating optical disk so that successive adjacent volumetric annular bands, or supertracks, of the optical disk may be read, ultimately permitting that data may be radiatively read from substantially the entire annulus of the optical disk.
During writing the detector array is replaced by a masked array of second illuminators. These second illuminators serve to radiatively illuminatexe2x80x94with a second frequency radiation transmitted through the doubly-telecentric afocal imaging systemxe2x80x94a portion of the planar radial cross-section, tilted relative to the plane of the optical disk, that is also illuminated by the first illuminator. The first and the second illuminator jointly radiatively illuminate a plane segment, tilted relative to the plane of the optical disk and located within the volume of the optical disk, with spatially and temporally coincident first and second frequency radiations sufficient to write, or read, as the case may be, the photochemical within selected voxels of this plane segment, andxe2x80x94importantlyxe2x80x94not elsewhere within the volume of the optical disk.
8. Performance of a Three-Dimensional Compact Disk (3-D CD) in Accordance with the Invention
A more detailed showing of the parameters and the performance of a present, and of a prospective, three-dimensional compact disk (3-D CD) in accordance with the invention is contained in section 5 of the DESCRIPTION OF THE PREFERRED EMBODIMENT of this specification. That showing follows as long discussion in section 4 of the DESCRIPTION OF THE PREFERRED EMBODIMENT of this specification as to why the present invention is able to achieve its rather awesome performance without requiring that the performance of present tracking and imaging methods and components be transcended, and, indeed, while permitting that the precision, accuracy and time responsiveness of these existing optical disk components and control systems need not be improved upon over present norms.
Accordingly, such a three-dimensional compact disk (3-D CD) in accordance with the present invention as may actually be realized circa 1998, and such a 3-D CD as might prospectively be realized with present technologies, have the following parameters and performances:
Expanded explanation of the origin, and significance, of these parameters is given in the DESCRIPTION OF THE PREFERRED EMBODIMENT portion of this specification.
These and other aspects and attributes of the present invention will become increasingly clear upon reference to the following drawings and accompanying specification.